This disclosure is related to the field of multiple layer panels (also referred to as multilayer glass laminate panels) having reduced levels of edge defects and optimized autoclave cycle conditions for producing improved multiple layer panels having at least one polymer interlayer sheet. Specifically, this disclosure is related to the field of optimized autoclave cycle conditions for producing improved multiple layer panels having at least one polymer interlayer sheet and having reduced levels of edge defects.
Multiple layer panels are generally panels comprised of two sheets of a rigid substrate (such as, but not limited to, glass, polyester, polyacrylate, or polycarbonate) with one or more polymer interlayers sandwiched therebetween. The laminated multiple layer glass panels are commonly utilized in architectural window applications, in the windows of motor vehicles and airplanes, and in photovoltaic solar panels. The first two applications are commonly referred to as laminated safety glass. The main function of the interlayer in the laminated safety glass is to absorb energy resulting from impact or force applied to the glass, to keep the layers of glass bonded even when the force is applied and the glass is broken, and to prevent the glass from breaking up into sharp pieces. Additionally, the interlayer may also give the glass a much higher sound insulation rating, reduce UV and/or IR light transmission, and enhance the aesthetic appeal of the associated window.
In order to achieve the desired and optimal sound insulation for the glass panel, it has become common practice to utilize interlayers having special properties. In some cases, multilayered interlayers with at least one soft “core” layer sandwiched between two more rigid “skin” layers are used as the interlayer in a multilayer glass laminate panel. These interlayers are generally produced by mixing a polymer resin such as poly(vinyl butyral) with one or more plasticizers and melt processing the mix into a sheet by any applicable process or method known to one of skill in the art, including, but not limited to, extrusion. For multilayer interlayers, the layers are generally combined by processes such as co-extrusion and lamination. Other additional ingredients may optionally be added for various other purposes. After the interlayer sheet is formed, it is typically collected and rolled for transportation and storage and for later use in the multiple layer glass panels, as discussed below.
Contemplated polymer interlayers include, but are not limited to, polyvinyl acetals (PVA) (such as polyvinyl butyral (PVB)), polyurethane (PU), poly(ethylene-co-vinyl acetate) (EVA), polyvinylchloride (PVC), polyethylenes, polyolefins, ethylene acrylate ester copolymers, poly(ethylene-co-butyl acrylate), silicone elastomers, epoxy resins, and acid copolymers such as ethylene/carboxylic acid copolymers and its ionomers, derived from any of the foregoing possible thermoplastic resins. Multilayer laminates can include multiple layer glass panels and multilayer polymer films. In certain embodiments, the multiple polymer films in the multilayer laminates may be laminated together to provide a multilayer film or interlayer. In certain embodiments, these polymer films may have coatings, such as metal, silicone or other applicable coatings known to those of ordinary skill in the art. The individual polymer films which comprise the multilayer polymer films may be laminated together using an adhesive as known to those of ordinary skill in the art.
The interlayer may be a single layer, a combination of more than one single layer, a multilayer that has been coextruded, a combination of at least one single layer and at least one multilayer, or a combination of multilayer sheets.
The following offers a simplified description of the manner in which multiple layer glass panels are generally produced in combination with the interlayers. First, at least one polymer interlayer sheet (single or multilayer) is placed between two substrates and any excess interlayer is trimmed from the edges, creating an assembly. It is not uncommon for multiple polymer interlayer sheets or a polymer interlayer sheet with multiple layers (or a combination of both) to be placed within the two substrates creating a multiple layer glass panel (also referred to herein as a multilayer glass laminate panel) with multiple polymer interlayers. Then, air is removed from the assembly by an applicable process or method known to one of skill in the art; e.g., through nip rollers, vacuum bag, vacuum ring or another de-airing mechanism. Additionally, the interlayer is partially press-bonded to the substrates by any method known to one of ordinary skill in the art. In a last step, in order to form a final unitary structure, this preliminary bonding (or adhesion) is rendered more permanent by a high temperature and pressure lamination process, or any other method known to one of ordinary skill in the art such as, but not limited to, autoclaving. Additional parameters and details of the autoclaving will be further discussed below.
One of the problems in the manufacture of multilayer laminate glass panels is the presence of edge defects, such as bubbles, in the final unitary structure or panel. The bubbles may be formed during the lamination process, after the lamination process while in storage or use, or both. These bubbles or edge defects are typically formed near the edge, such as from about 2 to 3 mm from the edge, of the glass panels. The edge bubbles are typically round shaped ranging from a few tenths of a millimeter to about one millimeter (about 0.1 mm or more to about 1 mm) in diameter. Other bubbles or edge defects can form at the very edge or further in from the edge of the glass panels. It is not uncommon for bubbles or edge defects to form five millimeters or more from the edge of the glass panels. The bubbles or edge defects cause optical defects in the final multilayer glass laminate panel, such as a windshield, affect edge integrity of the panel, affect the bonding of the interlayer to the glass substrates, and are unacceptable to the final customer.
One source for air or other gases accounting for edge bubbles is the de-airing process. During the manufacturing process of laminated multiple layer glass panels, air and other gases often become trapped in the interstitial spaces between the substrates and the interlayer or between the individual layers of the multilayered interlayer when these layers are stacked together to form the multilayered interlayer other than co-extrusion.
As noted above, trapped air is generally removed in the glazing or glass panel manufacturing process by vacuum or nip roll de-airing the construct. However, these technologies are not always effective in removing all of the air trapped in the interstitial spaces between the substrates. These pockets of air are particularly evident with mismatched glass (e.g., tempered glass, heat strengthened glass, and thick, annealed glass) and in windshields, where the curvature of the glass generally results in gaps of air. These gaps of air in windshields are commonly referred to as “bending gaps.” Additionally, when a bending gap is present during autoclaving, heat and pressure compress the glass to conform to the interlayer and narrow the gap, resulting in high stresses in the glass in the original gap area.
Since de-airing technologies are not always effective in removing all of the air from the glass panel assembly, there is normally residual air present between the glass and interlayer. During autoclaving, the residual air dissolves into the interlayer under heat (temperature) and pressure. When a large amount of residual air (e.g., excessive residual air) is present in the interlayer, air bubbles can nucleate, especially at high temperatures, as the interlayer becomes soft and is less resistant to the nucleation.
In warm or hot climates, especially during the summer season, the temperature of glass can elevate to 50° C. to 100° C. or more in multilayer glass laminate panels installed in buildings and vehicles. At these elevated temperatures, forces due to stresses in glass panels or windshields exert pressure on the glass perpendicularly to their plane and in the opposite direction, pulling the glass panels away from each other in an effort to restore them to their original states. This pressure or stress reduces the resistance of the air to nucleation and expansion, and it allows the bubbles to grow in the interlayer, particularly around the edges of the panel or windshield.
Another source for air or other gases accounting for edge bubbles is the autoclaving step or process. A typical autoclaving cycle involves the following steps: (1) heating and pressurizing the inside of the autoclave chamber (that is filled with multilayer glass laminate panels, such as windshields) to a pre-defined maximum temperature and pressure; (2) holding the temperature and pressure constant at the pre-defined maximum level for a period of time; (3) reducing the temperature while holding pressure constant; and (4) releasing the pressure to atmospheric pressure once the temperature reaches about ambient or room temperature. The temperature at which the autoclave pressure is released is commonly referred as pressure release temperature or pressure dump temperature. Optionally, during step (1), the pressure and temperature can gradually and simultaneously be increased; the temperature gradually increases first and is then followed by the pressure increasing or vice versa; or the temperature and pressure can be increased simultaneously first, then as the temperature continues to increase the pressure is held at a pressure level less than maximum for a short period of time before it is increased to the maximum pressure. During step (3), as the temperature is decreasing, the pressure can be decreased in steps rather than being held constant. Finally, during step (4), the pressure release temperature can be at room temperature or slightly above room temperature, generally in the range of about 30° C. to about 55° C. Regardless of how each of the steps can be changed, the maximum temperature (often referred as “soak temperature” or “hold temperature” or “autoclave temperature”), maximum pressure (often referred as “soak pressure” or “hold pressure” or “autoclave pressure”), and the time (often referred as “soak time” or “hold time” or “autoclave time”) at which the maximum temperature and pressure are held are three key parameters for fabricating a multilayer glass laminate panel or laminated safety glass to achieve the required properties and performance.
The conventional wisdom of autoclaving for producing multiple layer panels is to use as high a temperature and pressure as possible to promote the bonding (or adhesion) of an interlayer to the substrates and to remove the surface of the interlayer to promote better (or stronger) adhesion of the interlayer to the substrates. Conventionally, the typical autoclave temperature is above 140° C. or above 150° C., and the typical pressure is about 12 to 14 bars. The typical hold time at which the temperature and pressure stay at the maximum level can be about 20 minutes to about 60 minutes for multilayer glass laminate panels, such as windshields or side glass laminates (also referred to as “side lites”), and 20 minutes to several hours for multilayer glass laminate panels for laminated architectural glass where thicker glass and often thicker interlayers are used. As will be further discussed below, a significant amount of air is dissolved in the interlayer in the multilayer glass laminate panel during the autoclave process.
The presence of edge bubbles in the final unitary structure of a multilayer laminate glass panel can be problematic because a certain degree of optical quality and clarity is necessary in many (if not most) of the end-use commercial applications of multilayer laminate glass panels (e.g., vehicular, aeronautical and architectural applications). Thus, the creation of multilayer laminate glass panels with commercially acceptable levels of edge defects (that is, where the level of edge defects is very low, or particularly where edge bubbles are eliminated and there are no edge defects) is paramount in the art of multilayer glass laminate panel manufacturing.
Summarized, optical quality defects such as edge defects (or edge bubbles) and other visible optical defects, as well as edge integrity, are common problems in the field of multiple layer glass panels, particularly those used in applications which require higher levels of optical or visual quality and edge integrity. Accordingly, there is a need in the art for the development of a process for producing a multilayer glass laminate panel that resists or prevents the formation of edge bubbles during the autoclave cycle or after autoclaving without a reduction in other optical, mechanical, and acoustic characteristics of the multilayer laminate glass panel.